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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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OTHER GLACIERS OF PRINCE WILLIAM SOUND               387
The amount of glacial erosion below sea level in most of Orca Inlet is entirely concealed by deposits. The part of Orca Inlet from Cordova to the head has depths of from 90 to 228 feet east of Salmo Point, but is much shallower from that point to Cordova, with depths of from 6 to SO or 40 feet and with many shoals and a few navigable channels in which the maximum depth of water is 90 feet. Southwestward from Cordova the depth is generally 12 feet or less, excepting for one or two small discontinuous channels. Thus it is evident that Orca Inlet differs from all the other fiords in Prince William Sound, and indeed from most Alaskan fiords, in being shallow. It is a fiord nevertheless but one very much modified by deposition.
Glacial Deposits on the Land. Glacial deposits around Orca Bay and Orca Inlet are inconspicuous, being thin or absent because of the steepness of the fiord walls. Uncon-solidated till with striated, angular bowlders may be seen in a number of cliffs along the coast, near Cordova, and in the town. There are also small patches of outwash gravel* including several near the town of Cordova. The largest area where these are developed* so far as we know, is a large valley train, described to us by prospectors as occupying; the valley which leads northeastward, from the head of Orca Inlet Do the northern margin: of Shephard Glacier and the adjacent ice tongues. There are small terraces of outwash gravel on the mainland north of Orca Bay, and on the northern side of Hawkins Island at the narrowest portion of the Salmo Point peninsula.
Submerged Glacial Deposits. In these fiords the glacial deposits below sea level are the most extensive and we shall describe in order (1) the bottom deposits of Orca Bay,, which do not seem to form submerged moraines but mantle the bottom of the fiord, (2) the deposits which have filled up the larger part of Orca Inlet, and (8) the Middle Ground Shoal of Orca Bay, which is a tidal delta built by glacial marine deposits from Orca Inlet.
In the fiords of the northern and western sides of Prince William Sound, the deposits below sea level are imperfectly described, because, in connection with the soundings which we made, no samples of bottom material were collected. Accordingly, we have thus far discussed only glacial deposits on the sea bottom where they stood up as moraines. In Orca Bay and Orca Inlet the detailed Coast Survey charts furnish some indication of bottom material as well as depths. We can, therefore, describe, in a general way, the bottom deposits in Orca Bay, which seem to have been made by a greater glacier filling the whole fiord and which probably retreated eastward into the mountains northeast of Orca Inlet and the mountains northeast of the heads of Sheep and Simpson Bays. These deposits are all to be classed as glacial, for no sediment-laden streams of any size now enter Orca Bay. and the former rivers, whose deposits partly mantle the material dropped by the retreating glaciers and by floating icebergs, were all glacial streams.
In the eastern part of Orca Bay, from Bomb Point, to the Salmo Point Narrows the chart indicates rocky bottom and sand, a condition not found elsewhere in the fiord excepting close to the shore. This suggests a bottom veneer of morainic deposits. There are small patches of mud in mid-fiord.
From this point westward the fiord has a bottom of sticky or soft mud, evidently brought in by tidal currents, with hard material only rarely, and with rocky bottom only near shore.
The shallow western two-thirds of Orca Inlet has been so modified by filling that most of it is unnavigable, the filling having been largely done by tidal currents, which are